Structural timber floor assembly

ABSTRACT

A method is described of forming a joint between the end of a timber I-beam joist and a transverse closure such as a rim-joist, in which two holes are formed a short distance from the end of the I-beam to be butt-jointed to the rim-joist, one in each of the upper and lower rails of the I-beam section, the two holes being coaxial and generally aligned with and parallel to the web of the I-beam section. The closure is positioned relative to the I-beam and two further holes are formed through the closure and into the ends of the upper and lower I-beam rails, generally perpendicular to and intersecting the first two holes. Two cross-dowels are inserted into the two first holes, each having a transverse threaded opening, and the dowels are inserted so as to align the openings with the holes which intersect the holes containing the cross-dowels, and threaded bolts are introduced into the intersecting holes and screwed into the threaded openings in the cross-dowels so as to draw the joist towards the closure, and thereby clamp the joist thereto. The cross-dowels may be formed from metal, or from a rigid plastics material or from a composite material and may have a smooth exterior or may be externally threaded or formed with one or more annular barbs for securing them in place. The technique may be applied on site, but more preferably in the course of constructing a roofing or flooring panel off-site, the joints serving to resist distortion or bending during handling of prefabricated panels, during storage, transportation, and/or final positioning on site.

FIELD OF INVENTION

[0001] This invention concerns structural assemblies of timber whichserve as prefabricated roofs or floors (often referred to as decks) forbuildings, particularly but not exclusively, timber framed buildings.

BACKGROUND TO THE INVENTION

[0002] Prefabricated timber buildings are generally delivered to site inthe form of prefabricated wall panels and roof trusses. The ground floorwall panels, when erected, provide load-bearing supports for first-floorflooring, the peripheral regions of which will in general provide abearing for the first floor load bearing wall panels.

[0003] Timber I-beams are now used in the construction industry as analternative to solid timber beams, and comprise a thin vertical web,typically made from oriental strand board, and top and bottom chordmembers (rails or flanges) made from solid or laminated timber. TheI-beam section is more structurally efficient than a solid rectangularsection and can be made to larger dimensions than is available in solidtimber.

[0004] Originating in the USA more than 20 years ago, they are nowgaining acceptance in the UK and other European countries.

[0005] In most applications, these beams are used as a directreplacement for solid timber and are supplied to site as individualcomponents for assembly by site carpenters.

[0006] The assembly details are very similar to those used for solidtimber comprising mainly nails or screws for fixing members togetherwith the use of metal joist hangers for load bearing construction.

[0007] Thus each flooring-panel or deck is constructed on site interalia from a plurality of parallel spaced-apart fabricated timber I-beamjoists each formed from a narrow web of timber and upper and lower railsor flanges formed from laminated veneer lumber, routed to accommodatethe upper and lower edges of the web material. The I-beam joists arebutt-jointed to the joists (sometimes called rim-beams) which extendorthogonally to the rims of the I-beam joists, with the rim joistscross-nailed on site to the ends of the I-beams. Bracing between theI-beam joists resists lateral movement or tilting of the I-beam joists,and where appropriate the flooring panel or deck may include areas inwhich I-beam joists run perpendicularly to other I-beam joists, and arebutt-jointed at their ends to a rim-joist or another I-beam joist.

[0008] Such a structure is generally satisfactory when constructed onsite as a first floor deck, sandwiched between ground floor and firstfloor wall panels. However the handling of such flooring panels ordecks, after prefabrication, during storage, shipping from factory tosite, and when lifted (usually by crane) into position at first floorlevel, can result in twisting and distortion of the panels, generatingsignificant bending and shearing forces on the joints between thecomponent parts. The result is that the flooring panel can becomeweakened and in particular joints between the ends of the I-beam joistsand rim-joists can open-up.

[0009] It is an object of the present invention to provide an improvedmethod of connecting I-beam joists to orthogonal timber components suchas rim joists, to reduce the tendency for mis-handling and bending ofthe panel to open-up the joints between the joists.

SUMMARY OF THE INVENTION

[0010] According to the present invention a method of forming a jointbetween one end of a timber, flanged I-beam joist and a transverseclosure such as a rim-joist, wherein the I-beam joist is arranged sothat the web of the joist is generally vertical and the flanges of theI-beam sections are above and below the web comprises the steps of:

[0011] 1)forming two holes a short distance from the end of the I-beamwhich is to be butt-jointed to the closure, one hole in each of theupper and lower flanges of the flanged I-beam section,

[0012] 2) locating the closure in place and forming two further holestherethrough and into the abutting ends of the upper and lower flangesof the I-beam joist, the two further holes being generally perpendicularto, and intersecting, the first two holes,

[0013] 3) inserting two cross-dowels into the two first holes, eachhaving a transverse threaded opening, and aligning the threaded openingswith the intersecting holes, and

[0014] 4) inserting threaded bolts into the intersecting holes to engagein the threaded openings in the cross-dowels, and screwing the boltsinto the dowels so as to draw the abutting end of the I-beam joisttowards the closure, and thereby clamp it to the closure.

[0015] Where a roofing or flooring panel is comprised of two or moresuch I-beam joists in a parallel spaced apart array, with ends of theI-beam joists abutting a perpendicular closure or rim-joist, a similarjoint made up of two cross-dowels and co-operating bolts, is providedbetween the ends of each said I-beam joist and the rim-joists.

[0016] The cross-dowels may be formed from metal, or from a rigidplastics material or from a composite material.

[0017] The bolts are typically formed from metal or a rigid plasticsmaterial.

[0018] A load spreading washer may be located between the head of eachbolt and the rim-joist, or each bolt head may include an integral loadspreading flange for increasing the area of the bolt head which is tomake contact with the rim-joist.

[0019] The ends of the holes through the rim-joist through which thebolts pass into the rim-joist may be enlarged to accommodate the headsof the bolts, so that the latter are wholly contained within therim-joist.

[0020] Where the upper and lower rails (flanges) of the I-beam joist arelaminated, the holes which are to receive the cross-dowels preferablyextend generally perpendicular to the laminations.

[0021] The invention also lies in a prefabricated timber roofing orflooring panel or deck, constructed inter alia from parallel spacedapart laminated timber I-beam joists butt-jointed to the side faces ofperpendicularly extending rim-joists at opposite ends of the I-beamjoists, wherein the joints between the ends of the I-beam joists and therim-joists are formed by bolts and cross-dowels, wherein the latterextend perpendicularly to the laminations forming the upper and lowerrails (flanges) of the I-beam joists and the bolts extend transverselythrough the rim-joists and are threadedly engaged in the cross-dowels.

[0022] The invention also lies in a laminated timber I-beam joist havingcross-dowels located transverse to the direction of the laminationsforming the upper and lower rails (flanges) of the I-beam section, closeto at least one end thereof, to enable the I-beam to be butt-jointed toa transversely extending rim-joist by means of bolts which in use extendthrough the rim-joist for threaded engagement in the cross-dowels in theI-beam joist.

[0023] The invention also lies in a cross-dowel adapted to be secured ina laminated flange of a timber I-beam joist, wherein the dowel isgenerally cylindrical in configuration and is formed an external screwthread profile the external diameter of which increases from the end ofthe dowel which is to be first introduced into the hole in the laminatedflange, towards the other end thereof, and the said other end includes ascrewdriver slot or other tool engaging means, to enable it to bescrewed into the hole in the laminated flange of the I-beam joist.

[0024] The screw thread may be of the self-tapping variety.

[0025] The invention also lies in a cross-dowel adapted to be secured ina laminated flange of a timber I-beam joist, wherein the externalsurface of the dowel is formed with at least one annular barb, andpreferably a plurality of such annular barbs, in the form of a fir tree,the external diameter of the barbs increasing from the end which isfirst intruded into the hole in the laminations, towards the other endthereof, whereby in use the dowel may be secured in the laminated railby introducing the barbed end into a pre-formed hole in the laminatedflange and driving the dowel into the hole using a hammer or mallet or apower driver.

[0026] Preferably the end of the dowel which is visible even after ithas been driven into the flange of the I-beam joist, is formed with ascrewdriver slot or other means whereby it can be rotated whilstembedded in the flange, to enable the transverse threaded openingtherein to be aligned to receive a rim-joist securing bolt.

[0027] It has been found in practice that a roof or flooring panelconstructed in accordance with the invention is less susceptible todistortion damage during handling, storage and/or shipment, than aresimilar flooring panels when constructed using conventionalcross-nailing techniques.

[0028] A cross-dowel connection may be formed between the end of onerim-joist and an abutting face of an adjoining rim-joist at a corner ofa roof or flooring panel embodying the invention.

[0029] The invention thus allows timber I-beams to be constructed intolarger building sections. Thus for example, beams and sheeting can bemade up into larger prefabricated floor decks or roofing panels anddelivered to site for lifting into position by crane.

[0030] Site assembly techniques using nails, screws and metal joisthangers do not provide the strength and rigidity suitable for largeprefabricated components subject to the loads imposed during handlingand lifting. These loads are different from those encountered on siteand in situ and require joints with additional rigidity and strength.

[0031] The invention provides a solution to these problems for use atthe junction of I-beams with supporting rimboards or rim-joists and forthe first time it is now possible to industrialise the assembly processof roofing and flooring decks etc.

[0032] The invention will now be described by way of example withreference to the accompanying drawing in which:

[0033]FIG. 1 is an exploded perpendicular view of a joint between theend of a timber I-beam joist and a rim-joist, embodying the invention;

[0034]FIG. 2 illustrates a cross-dowel, suitable for use in the joint ofFIG. 1;

[0035]FIG. 3 shows the initial stages of making the joint of FIG. 1; and

[0036]FIG. 4 shows the completed joint.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENT

[0037] In FIG. 1 a timber I-beam joist 10 is shown formed from arelatively thin vertical web of timber/timber composite material 12, theupper and lower longer edges of which are adhesively bonded into routedgrooves in the upper and lower flanges or rails 14, 16 each of which isformed by laminating a larger number of thin strips of timber, thelaminations running parallel to the length dimension of the beam (asshown) and the stack being orientated generally at right angles to theweb 12. The laminations are denoted by reference numeral 18 in the caseof the upper flange 14 and by 20 in the case of the lower rail 16.

[0038] The end of the beam is cut square so that the cut ends 22, 24 ofthe upper and lower rails occupy the same plane as does the cut end 26of the web 12.

[0039] A timber rim joist 28 is to be butt-joined to the end faces 22,24, 26 of the I-beam joist 10.

[0040] In accordance with the invention holes are formed in the upperand lower rails (only the upper one 30 being visible in FIG. 1) andcross-dowels such as 32, 33 are located in each of the two holes, with athreaded transverse openings 34, 35 in the dowels aligned withorthogonal holes 36 and 38 which intersect the holes in the upper andlower flanges.

[0041] The joint is completed by inserting two threaded bolts 40, 42through two pre-drilled holes 44, 46 in the rim-joist 38, so as to enterand pass through the holes 36 and 38 respectively, to engage in thethreaded transverse openings (such as 34 in the case of dowel 32) in thedowels. Tightening the bolts into the dowels draws the rim-joist into atight fit on the ends 22, 24, 26 of the I-beam joist 10.

[0042] A typical cross-dowel cast and machined from metal, is shown at48 in FIG. 2.

[0043]FIGS. 3 and 4 show in cross section how the bolt 42 and dowel 33fit into the orthogonal holes 38 and 39 respectively.

[0044] Both holes 38 and 38 are conveniently formed by drilling and bothare drilled beyond the region in which the two holes intersect, so as toaccommodate the driven ends of the dowel and bolt respectively.

[0045] It is to be understood that the head of the bolt may be more likea flat nail head, to reduce the need for undercutting the hole 38. Inthis event a screwdriver slot (which may to advantage be a crossed slotto receive a cross-headed screwdriver) is formed in the end face of thehead of the bolt.

[0046] Although not shown the dowel may be tapered and/or formed withannular rims to create a barbed or firtree connection with the timberjoist.

1. A method of forming a butt joint between one end of a timber, flangedI-beam joist and a transverse closure such as a rim-joist, wherein theI-beam joist is arranged so that the web of the joist is generallyvertical and the flanges of the I-beam section are above and below theweb, comprising the steps of: 1) forming two holes a short distance fromthe end of the I-beam which is to be butt-jointed to the closure, onehole in each of upper and lower flanges of the flanged I-beam section,2) locating the closure in place and forming two further holestherethrough and into the abutting ends of the upper and lower flangesof the I-beam joist, the two further holes being generally perpendicularto, and intersecting, the first two holes, 3) inserting two cross-dowelsinto the two first holes, each having a transverse threaded opening, andaligning the threaded openings with the intersecting holes, and 4)inserting threaded bolts into the intersecting holes to engage in thethreaded openings in the cross-dowels, and screwing the bolts into thedowels so as to draw the abutting end of the I-beam joist towards theclosure, and thereby clamp it to the closure.
 2. A building panelcomprised of at least two I-beam joists and at least one perpendicularclosure, the I-beam joists forming a parallel spaced apart array, withends of the I-beam joists abutting the perpendicular closure, with abutt joint between the end of each of the I-beam joists and the closure,characterised by: 1) two holes formed a short distance from the end ofthe I-beam which is to be butt-jointed to the closure, one hole in eachof upper and lower flanges of the flanged I-beam section, 2) two furtherholes through the abutting ends of the upper and lower flanges of theI-beam joist, the two further holes being generally perpendicular to,and intersecting, the first two holes, 3) two cross-dowels located inthe two first holes, each having a transverse threaded opening alignedwith the intersecting holes, and 4) threaded bolts engaged in andscrewed into the threaded openings in the cross-dowels, so that theabutting end of the I-beam joist is drawn towards the closure, therebyto clamp it to the closure.
 3. A building panel according to claim 2wherein a load spreading washer is located between the head of each boltand the closure.
 4. A building panel according to claim 2 wherein eachbolt head includes an integral load spreading flange for increasing thearea of the bolt head which is to make contact with the closure.
 5. Abuilding panel according to claim 2 wherein the holes through theclosure through which the bolts pass into the I-beam are enlarged at oneend to accommodate the heads of the bolts, so that the latter are atleast partly contained within the thickness of the closure.
 6. Abuilding panel according to claim 2 wherein the upper and lower flangesof the I-beam joist are laminated, and the holes which are to receivethe cross-dowels extend generally perpendicular to the laminations.
 7. Abuilding panel according to claim 6 wherein the holes in the upper andlower flanges are generally aligned with the web of the I-beam section.8. A building panel according to claim 6 wherein the holes in theflanges are co-axial.
 9. A prefabricated timber building panel or deck,constructed from parallel spaced apart laminated timber I-beam joistsbutt-jointed to the side faces of perpendicularly extending rim-joistsat opposite ends of the I-beam joists, wherein the joints between theends of the I-beam joists and the rim-joists are formed by bolts andcross-dowels, wherein the latter extend perpendicularly to thelaminations forming the upper and lower flanges of the I-beam joists,and the bolts extend transversely through the rim-joists and arethreadedly engaged in the cross-dowels.
 10. A laminated timber I-beamjoist comprising a web between upper and lower laminated flanges, havingcross-dowels located therein transverse to the direction of thelaminations close to at least one end thereof, to enable the I-beam tobe butt-jointed to a transversely extending closure by means of boltswhich in use extend through the closure and are threadly engaged in thecross-dowels in the I-beam joist.
 11. A cross-dowel adapted to besecured in a laminated flange of a timber I-beam joist to enable theI-beam joist to be secured to a closure in accordance with the method ofclaim 1, wherein the dowel is generally cylindrical in configuration, isformed with an external screw thread profile, and one end of the dowelincludes tool engaging means to enable it to be screwed into a hole inthe laminated flange of the I-beam joist.
 12. A cross-dowel according toclaim 11 wherein the external screw thread profile is a self-tappingthread.
 13. A cross-dowel according to claim 11, wherein the externaldiameter of the screw thread profile increases from the end of the dowelwhich is to be first introduced into the hole in the laminated flange,towards the other end which includes the tool engaging means.
 14. Across-dowel adapted to be secured in a laminated flange of a timberI-beam joist to enable the I-beam joist to be secured to a closure inaccordance with the method of claim 1, wherein the external surface ofthe dowel is formed with at least one annular barb for retaining thedowel in a hole in the laminated flange.
 15. A cross-dowel according toclaim 14 wherein the dowel is formed at one end with a tool engagingmeans such as a screwdriver slot whereby it can be rotated whilstembedded in the flange, to enable the transverse threaded openingtherein to be aligned to receive a securing bolt.
 16. A flooring orroofing panel according to claim 2 wherein the panel edges are formed byelongate closures, and a cross-dowel connection is formed between theend of one closure and an abutting face of an adjoining closure at eachcorner of the panel.